(1) Field of the Invention
This invention relates to a low hydrogen type coated electrode, and more particularly to a low hydrogen type coated electrode which produces excellent effects when applied to downward welding for circumferential butt joints of pipes.
(2) Description of the Prior Art
Site welding of circumferential butt joints in pipelines has conventionally been carried out by downward welding techniques using coated electrodes, which have been of the low hydrogen type or ilmenite type in Japan and of the cellulose type in other countries. Because hydrogen-induced cracking is a major problem in welding of high-tensile steel pipes, especially in the case of site welding carried out in a cold place, it is desirable to use low hydrogen type coated electrodes. However, it has been very difficult to achieve downward welding by use of the conventional low hydrogen type coated electrodes.
To overcome the above difficulties, the present inventors have previously proposed Japanese Patent Publication No. 56-21519 (1981).
However, the low hydrogen type coated electrode according to the above-mentioned proposal, though having far more excellent performance as compared with the previous ones, are yet unsatisfactory and need improvements in view of the recent requests for higher efficiency and performance for use under severer conditions.
That is, when the low hydrogen type coated electrode according to the above proposal is used for downward welding of a circumferential butt joint in a piping, the conformability of the bead to the parent metal may become insufficient in welding the portion ranging from 4.5 to 6 o'clock (8.5 to 6 o'clock) positions as shown in FIG. 1. The insufficient conformability necessitates after-treatments such as grinder work.